Tegument protein UL21 of alpha-herpesvirus inhibits the innate immunity by triggering CGAS degradation through TOLLIP-mediated selective autophagy

A bacterial RING ubiquitin ligase triggering stepwise degradation of BRISC via TOLLIP-mediated selective autophagy manipulates host inflammatory response

Numerous bacterial pathogens have evolved tactics to interfere with the host ubiquitination network to evade clearance by the innate immune system. Nevertheless, the subtle antagonism between a bacterial ubiquitinase and a host deubiquitinase, through which they modify their respective targets within a multifaceted network, has yet to be characterized. BRCC3 isopeptidase complex (BRISC) is a newly identified K63-specific deubiquitinase complex that plays a crucial role in cellular signaling pathways such as inflammation. NleG, a type III secretion system (T3SS) effector, contains a conserved RING E3 ubiquitin ligase domain that interacts with host ubiquitination machinery, along with a distinct substrate-recognition domain that targets host proteins. Here, one particular variant, NleG6, was identified as mediating K27- and K29-linked polyubiquitination at residues K89 and K114 of ABRAXAS2/FAM175B, a scaffolding protein within the BRISC complex, leading to its degradation through TOLLIP (toll interacting protein)-mediated selective autophagy. Further investigations elucidated that ABRAXAS2 degradation triggered the subsequent degradation of adjacent BRCC3, which in turn, hindered TNIP1/ABIN1 degradation, ultimately inhibiting NFKB/NF-κB (nuclear factor kappa B)-mediated inflammatory responses. This chain of events offers valuable insights into the NFKB activation by the K63-specific deubiquitinating role of BRISC, unveiling how bacteria manipulate ubiquitin regulation and selective autophagy within the BRISC network to inhibit the host's inflammatory response and thus dominate a pathogen-host tug-of-war.Abbreviations: 3-MA: 3-methyladenine; A/E: attaching and effacing; ATG7: autophagy related 7; BafA1: bafilomycin A1; BNIP3L/Nix: BCL2 interacting protein 3 like; BRISC: BRCC3 isopeptidase complex; Cas9: CRISPR-associated system 9; co-IP: co-immunoprecipitation; CQ: chloroquine; CRISPR: clustered regulatory interspaced short palindromic repeat; DAPI: 4',6-diamidino2-phenylindole; DMSO: dimethyl sulfoxide; DUB: deubiquitinating enzyme; E. coli: Escherichia coli; EHEC: enterohemorrhagic Escherichia coli; EPEC: enteropathogenic Escherichia coli; GFP: green fluorescent protein; LEE: locus of enterocyte effacement; MAP1LC3B/LC3: microtubule associated protein 1 light chain 3 beta; MG132: cbz-leu-leu-leucinal; MOI: multiplicity of infection; NBR1: NBR1 autophagy cargo receptor; NC: negative control; NFKB/NF-κB: nuclear factor kappa B; NH4Cl: ammonium chloride; OPTN: optineurin; SQSTM1/p62: sequestosome 1; sgRNAs: small guide RNAs; T3SS: type III secretion system; TNF: tumor necrosis factor; TOLLIP: toll interacting protein; TRAF: TNF receptor associated factor; TUBB: tubulin beta class I; WCL: whole cell lysate; WT: wide type.

Duck plague virus US3 kinase phosphorylates and induces STING degradation to inhibit innate immune responses

Duck plague virus (DPV) causes the highest mortality rate among aquatic birds; however, its antago nistic mechanism against antiviral innate immune responses remains elusive. In this study, we systematically screened and found that most DPV genes have inhibitory potential for duck cyclic guanosine monophosphate-adenosine monophosphate synthetase (cGAS)/stimulator of interferon (IFN) gene (STING) pathway-mediated antiviral responses, with the DPV US3 kinase showing the strongest inhibitory activity. Co-immunoprecipitation and immunoblotting assays demonstrated that DPV US3 interacted with STING and induced its degradation. Further mutagenesis experiments revealed that DPV US3 kinase activity was essential for phosphorylating STING, reducing STING dimerization, and inhibiting STING-mediated antiviral responses. Sequence alignment and mutagenesis studies have demonstrated that DPV US3 phosphorylates STING at serine 86, near the Endoplasmic reticulum (ER) retention sequence (R82YRGS86), disrupting its association with tank-binding kinase 1 (TBK1) and inducing STING degradation. Finally, US3 knockout attenuated DPV replication by activating higher levels of IFN and ISGs in vitro and in vivo. These results demonstrate that DPV promotes viral infection and pathogenicity by inducing STING degradation through the encoded US3 kinase, providing new insights into the mechanism of DPV immune evasion.

Zebrafish fkbp5 attenuates antiviral innate immunity by autophagic degradation of transcription factor irf7

Activation of the type I interferon (IFN-I) signaling pathway is crucial for protecting host cells against viral infections. IFN-I production requires the transcription factors IFN regulatory factor 3 (IRF3) and IRF7, and its regulation must be finely tuned to both combat infection effectively and prevent excessive immunopathology. Here, we report that selective autophagy mediated by zebrafish FK506-binding protein 5 (Fkbp5), a PPIase (peptidyl-prolyl isomerase) promotes the degradation of Irf7 and Irf3, thereby inhibiting virus-induced type I IFN production. Quantitative real-time reverse-transcription polymerase chain reaction experiments indicate that zebrafish fkbp5 is induced by viral infection. Moreover, disrupting fkbp5 in AB-line zebrafish using CRISPR/Cas9 enhances survival rates and reduces viral messenger RNA levels compared with wild-type zebrafish. In cell culture, using promoter analysis and quantitative real-time reverse-transcription polymerase chain reaction, we found fkbp5 overexpression significantly attenuates cellular antiviral capacity and facilitates viral proliferation. Mechanistically, we found that fkbp5 inhibits Irf3/7-induced IFN activation, which depends on the binding of Fkbp5 to the Irf3 or IRF association domain of Irf7 via co-immunoprecipitation and Western blot assays. Furthermore, Fkbp5 induces the autophagic degradation of Irf3 and Irf7 independent of its PPIase activity. Blocking autophagy in vivo and in vitro restores the regulation of the RLR (RIG-I-like receptor) pathway by fkbp5. These findings reveal a critical role for zebrafish fkbp5 in suppressing the activation of Irf7 and Irf3 for IFN signaling and antiviral immune responses.

Tollip deficiency enhances mitophagy and reduces STING activation in influenza A virus-infected mice

Toll-interacting protein (Tollip) is an intracellular adaptor protein with diverse functions including regulation of autophagy of mitochondria-mitophagy. Tollip deficiency promotes viral infection, but whether mitophagy is involved remains unclear. We sought to determine if mitophagy and associated signaling such as mitochondrial DNA (mtDNA) release and activation of stimulator of interferon genes (STING) contribute to worsened viral infection due to Tollip deficiency. Wild-type and Tollip knockout (KO) C57/BL6 mice were intranasally infected with influenza A virus (IAV), and then treated with or without a STING agonist 2'3'cGAMP for 4 d. PINK1 (an initiator of mitophagy) KO mouse tracheal epithelial cells (mTECs) or PINK1 KO mice were infected with IAV to reveal the role of mitophagy in viral infection. In IAV-infected mice, Tollip deficiency enhanced lung mitophagy (more PINK1 and BNIP3L, but less p62), and decreased release of mtDNA. Furthermore, Tollip deficiency suppressed STING activation and the antiviral response (eg IFN-β and MX1), and increased viral load. In IAV-infected Tollip KO mice, 2'3'cGAMP activated STING and increased antiviral response coupled with less virus. PINK1-deficient mice increased lung release of mtDNA and augmented STING activation and antiviral responses. PINK1 deficiency in mTECs increased STING activation and significantly decreased the viral load. Our findings suggest that enhanced mitophagy due to Tollip deficiency reduces mtDNA release and STING activation during viral infection, resulting in decreased antiviral responses. Reduction of mitophagy and/or STING activation may open novel avenues for therapeutic intervention in human subjects with Tollip deficiency and viral infection.

Tracking of single virus: Dual fluorescent labeling of pseudorabies virus for observing entry and replication in the N2a cells

Pseudorabies virus (PRV) is a neurotropic herpesvirus. It is not easy to be track the whole replication progress of PRV, especially the nascent viral genome in the host cells. In this study, we developed a dual-fluorescence-labeled PRV (rPRV-Anchor3-mCherry) with the viral genome and the envelope protein gM labeled by ANCHOR DNA labeling system and mCherry, respectively. Through single-virus tracking of rPRV-Anchor3-mCherry, we observed that PRV invaded mouse neuroblastoma Neuro-2a cells via both endocytosis and plasma membrane fusion pathway. During the replication stage, parental and progeny viral genome of rPRV-Anchor3-mCherry in the cell nuclei could be visible, and viral nucleocapsid appeared more specifically than traditional capsid protein labeled PRV particles (rPRV-VP26-EGFP). We found that numerous progeny viral particles were produced in the nuclear, causing the nucleus membrane to break using three-dimensional (3D) live-cell imaging and electron microscopy. Moreover, our findings confirmed that simultaneously targeting of the UL9 and UL54 genes using a CRISPR-Cas9 system led to the complete inhibition PRV replication. rPRV-Anchor3-mCherry can be used to research multiple steps of the viral cycle.

Hepatitis B surface antigen hijacks TANK-binding kinase 1 to suppress type I interferon and induce early autophagy

There are close links between innate immunity and autophagy. However, the crosstalk between innate immunity and autophagy in host cells infected with hepatitis B virus (HBV) remains unclear. Here, we reported that HBsAg suppressed type I interferon production and induced the accumulation of autophagosomes. HBsAg boosted TANK-binding kinase 1 (TBK1) phosphorylation and depressed interferon regulatory factor 3 (IRF3) phosphorylation ex vivo and in vivo. Mechanistic studies showed that HBsAg interaction with the kinase domain (KD) of TBK1 augmented its dimerization but disrupted TBK1-IRF3 complexes. Using the TBK1 inhibitor, BX795, we discovered that HBsAg-enhanced TBK1 dimerization, promoting sequestosome-1 (p62) phosphorylation, was necessary for HBV-induced autophagy and HBV replication. Moreover, HBsAg blocked autophagosome-lysosome fusion by inhibiting the synaptosomal-associated protein 29 (SNAP29) promoter. Notably, liver tissues from HBsAg transgenic mice or chronic HBV patients revealed that IFNβ signaling was inhibited and incomplete autophagy was induced. These findings suggest a novel mechanism by which HBsAg targets TBK1 to inhibit type I interferon and induce early autophagy, possibly leading to persistent HBV infection. Molecular mechanisms of HBsAg suppression of the IFNβ signaling pathway and triggering of early autophagy. HBsAg targets the kinase domain of TBK1, thereby disrupting the TBK1-IRF3 complex and inhibiting type I interferon production. On the other hand, HBsAg enhances TBK1 dimerization and phosphorylation, which upregulates the phosphorylation of p62 to induce p62-mediated autophagy. Furthermore, HBV infection causes the accumulation of autophagosomes. This is achieved by HBsAg suppressing the SNAP29 promoter activity, which blocks autophagosome-lysosome fusion.

TOLLIP inhibits the replication of PEDV by autophagic degradation of Nsp9

Selective autophagy plays a crucial role in innate antiviral immunity by targeting essential viral components and host factors necessary for virus propagation. Among these factors, the nonstructural protein 9 (Nsp9) of Porcine Epidemic Diarrhea Virus (PEDV) is required for viral replication. However, the host factors regulating Nsp9 have remained elusive. In our study, we discovered that Nsp9 undergoes degradation through selective autophagy. Using coimmunoprecipitation combined with mass spectrometry analysis, we identified Toll-interacting protein (TOLLIP) as an autophagy cargo receptor binding to Nsp9 and facilitating its autophagic degradation. Additionally, we found that TOLLIP interacts with LC3A, LC3C, and GABARAPL1. Further investigations revealed that Nsp9 specifically enhances the binding of TOLLIP to LC3A, rather than LC3C or GABARAPL1. Importantly, TOLLIP promotes the engulfment of Nsp9 by LC3A-coated autophagosomes and mediates Nsp9 trafficking to lysosomes, ultimately leading to LC3A-dependent degradation of Nsp9. Consequently, TOLLIP suppresses PEDV replication. Overall, our findings highlight the role of TOLLIP in connecting viral proteins to LC3A-dependent autophagosome, emphasizing its significance in combating viruses through selective autophagy.

ASFV pS183L protein negatively regulates RLR-mediated antiviral signalling by blocking MDA5 oligomerisation

The retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are major sensors against viral infection, but their roles in DNA virus infection largely remain unknown. This study found that a previously uncharacterised protein, pS183L, negatively regulates RLR signalling by suppressing MDA5 oligomerisation. Specifically, we showed that the overexpression of pS183L suppresses MDA5 but not cGAS-STING or RIG-I-induced IFN-β activation. Consistently, pS183L inhibited high molecular weight poly (I:C) activated IFN-β production. Furthermore, we demonstrated that pS183L interacts with CARDs and the MDA5 Helicase domain, consequently blocking MDA5 oligomerisation and the MDA5-MAVS interaction. Taken together, we concluded that pS183L blocks MDA5 oligomerisation through protein-protein interaction and thus disrupts MDA5-mediated IFN-β signalling.

The alpha-coronavirus E protein inhibits the JAK-STAT pathway signaling by triggering STAT2 degradation through OPTN- and NBR1-mediated selective autophagy

The zoonotic transmission of coronaviruses continues to pose a considerable threat to humans. Swine acute diarrhea syndrome coronavirus (SADS-CoV), a bat coronavirus related to HKU2, causes severe economic losses in the pig industry and has the potential to trigger outbreaks in humans. However, our understanding of how SADS-CoV evades the host's innate immunity remains limited, hindering effective responses to potential human outbreaks. In this study, we demonstrate that the SADS-CoV envelope protein (E) inhibits type I interferon (IFN-I) signaling by inducing the degradation of STAT2 via the macroautophagy/autophagy-lysosome pathway. Mechanistically, the E protein evades host innate immunity by promoting STAT2 degradation through autophagy, mediated by the NBR1 and OPTN receptors. Notably, ubiquitination of E protein is required for the autophagic degradation of STAT2. Additionally, lysine residue K61 of the E protein is crucial for its stable expression; however, it is not involved in its ubiquitination. In conclusion, our study reveals a novel mechanism by which the E protein disrupts IFN-I signaling by targeting STAT2 via autophagy, enhancing our understanding of SADS-CoV's immune evasion strategies and providing potential drug targets for controlling viral infections.Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; BafA1: bafilomycin A1; BSA: bovine serum albumin; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CC: coiled-coil; CHX: cycloheximide; Co-IP: co-immunoprecipitation; DAPI: 4',6-diamidino-2-phenylindole; DBD: DNA-binding domain; DMEM: Dulbecco's Modified Eagle's medium; DMSO: dimethyl sulfoxide; E, Envelope. FW: four-tryptophan; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HA: hemagglutinin; hpt: hours post-treatment; IF: indirect immunofluorescence; IFNB/IFN-β: interferon beta; IgG: immunoglobulin G; ISG: IFN-stimulated genes; ISRE: interferon-stimulated response element; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PBS: phosphate-buffered saline; PRRs: pattern recognition receptors; qPCR: quantitative polymerase chain reaction; SAR: selective autophagy receptor; SQSTM1/p62: sequestosome 1; STAT: signal transduction and activator of transcription; TBS-T: Tris-buffered saline with Tween 20; TCID50: 50% tissue culture infective dose; TOLLIP: toll interacting protein; Ub: ubiquitin; UBA: C-terminal ubiquitin-associated; VSV: vesicular stomatitis virus; WB: western blotting. WT: wild type.

IDR-driven TOLLIP condensates antagonize the innate antiviral immunity by promoting the deSUMOylation of MAVS

Mitochondrial antiviral signaling protein (MAVS) is a central adaptor protein in retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling against RNA viral infection. Posttranslational modifications (PTMs) play a critical role in modulating the activity of MAVS. However, how phase separation regulates the PTMs to fine-tune MAVS activation remains to be elucidated. In this study, we identify Toll-interacting protein (TOLLIP) as a negative regulator of RLR signaling. A deficiency of TOLLIP leads to an enhanced type I interferon response upon RNA viral infection. Mice with the deletion of TOLLIP are more resistant to lethal vesicular stomatitis virus (VSV) infection than wild-type counterparts. Mechanistically, TOLLIP forms condensates that rely on its intrinsically disordered region (IDR). TOLLIP condensates interact with SENP1, promote the aggregation of SENP1, and enhance the interaction between SENP1 and MAVS, consequently leading to deSUMOylation and less aggregation of MAVS. Overall, our study reveals the critical role of TOLLIP condensation in regulating the activation of MAVS, emphasizing the complexity of MAVS activity modulation.

The loss of both pUL16 and pUL21 in HSV-1-infected cells alters capsid-tegument composition, nuclear membrane architecture, cytoplasmic maturation and cell-to-cell spread

Previously, we had developed synthetic genomics methods to assemble an infectious clone of herpes simplex virus type-1 (HSV-1) strain KOS. To do this, the genome was assembled from 11 separate cloned fragments in yeast using transformation-associated recombination. Using this method, we generated null mutations in five tegument protein-coding genes as well as different combinations of these mutants. The single-locus mutants were all able to plaque on Vero cells. However, one multi-locus combination, ∆UL16/UL21, proved lethal for virus replication in non-permissive cells. The proteins encoded by the genes UL16 and UL21 are of interest because they are known to physically interact and are constituents of the tegument structure. Furthermore, their roles in HSV-1-infected cells are unclear. Both are dispensable for HSV-1 replication; however, in HSV-2, their mutation results in nuclear retention of assembled capsids and has activities that impact nuclear membrane integrity as well as activities of proteins that function in nuclear egress. We thus characterized these HSV-1 viruses that carry the single and double mutants. What we found was that the single mutants could replicate within cells and spread from infected to uninfected cells, albeit at significantly reduced levels. However, the double mutant (∆16/21) could not produce infectious progeny in a 24 h growth cycle and could not spread from cell to cell. Confocal microscopy of VP16-Venus expressed by these viruses as well as immunofluorescence assays for glycoprotein B showed perturbation of the nuclear membrane, which was pronounced in ∆21 and ∆16/21 infected cells. All the mutants assembled DNA-filled capsids as judged by ultrastructural analyses and sedimentation studies. Electron microscopy revealed the presence of numerous mature viruses in WT-infected cells but fewer such particles in the ∆16- and ∆21-infected cells. What we discovered is that in cells where both pUL16 and pUL21 are absent, cytoplasmic capsids were evident, but mature enveloped particles were not detected. The capsid particles isolated from all the single- and multi-locus mutant-infected cells showed significantly lower levels of incorporation of both VP16 and pUL37 when compared to the WT capsids. This reduced incorporation may be related to the loss of the integrity of the architecture of the nuclear membrane. Interestingly, the incorporation of pUL16 was not affected by the absence of pUL21 and vice versa, as judged by immunoblots. These data now show that of the tegument proteins, like the essential pUL36, pUL37 and VP16, the complex of pUL16 and pUL21 should be considered as important mediators of maturation and cell-to-cell spread of the particle.

Grass carp reovirus VP4 manipulates TOLLIP to degrade STING for inhibition of IFN production

Although fish possess an effective interferon (IFN) system to defend against viral infection, grass carp reovirus (GCRV) still causes epidemic hemorrhagic disease and tremendous economic loss in grass carp. Therefore, it is necessary to investigate the immune escape strategies employed by GCRV. In this study, we show that the structural protein VP4 of GCRV (encoded by the S6 segment) significantly restricts IFN expression by degrading stimulator of IFN genes (STING) through the autophagy-lysosome-dependent pathway. First, overexpression of VP4 inhibited the expression of IFN induced by GCRV and polyinosinic-polycytidylic acid (poly I:C) at both the promoter and mRNA levels. Second, VP4 was found to associate with STING, and the N-terminal transmembrane domain is essential for this interaction. Additionally, VP4 dramatically blocked STING-induced IFN expression and weakened its antiviral capacity. Further mechanistic studies revealed that VP4 degrades STING via the autophagy-lysosome pathway in a dose-dependent manner. Interestingly, toll-interacting protein (TOLLIP), a selective autophagy receptor, was found to interact with VP4 and reduce VP4-mediated STING degradation after tollip knockdown. Finally, overexpression of VP4 facilitated GCRV proliferation, while its depletion had the opposite effect. These findings indicate that GCRV VP4 recruits TOLLIP to degrade STING and achieve immune escape. This enhances our comprehension of aquatic virus pathogenesis.

IMPORTANCE

Upon virus invasion, fish cells employ a multitude of strategies to defend against infection. Consequently, viruses have evolved a plethora of tactics to evade host antiviral mechanisms. To date, fewer studies have been conducted on the immune evasion mechanism of grass carp reovirus (GCRV). In this study, we demonstrate that VP4 of GCRV-873 inhibits interferon expression by interacting with stimulator of IFN gene and degrading it in an autophagy-lysosome-dependent manner through the manipulation of the selective autophagy receptor toll-interacting protein. The findings of this study contribute to our understanding of the novel evasion mechanisms of GCRV and widen our knowledge of the virus-host interactions in lower vertebrates.

Post-translational modifications as a key mechanism for herpes simplex virus type I evasion of host innate immunity

Herpes simplex virus type 1 (HSV-1) is a DNA virus that infects humans and establishes long-term latency within the host. Throughout its prolonged interaction with the host, HSV-1 evades the innate immune system by encoding its own proteins. Post-translational modifications (PTMs) of these proteins play crucial roles in their function, activity, and interactions with other factors by modifying specific amino acids, thereby enabling a diverse range of protein functions. This review explores the mechanisms and roles of PTMs in HSV-1-encoded proteins, such as phosphorylation, ubiquitination, deamidation, and SUMOylation, during HSV-1 infection and latency. These modifications are essential for suppressing host innate immunity, facilitating viral replication, and elucidating the crosstalk among various post-translational modifications.

Ammonium chloride mitigates the amplification of fish virus by blocking autophagy-dependent replication

Ammonia fertilizer, primarily composed of ammonium chloride, is widely used in pond fish farming throughout Asia. Despite the belief that it possesses antiviral properties, the underlying mechanisms remain unclear. Ammonium chloride (NH4Cl) has been demonstrated to act as a potent inhibitor of autophagy, which is used by many fish viruses to promote their proliferation during infection. It was therefore hypothesized that the antiviral effect of ammonia fertilizers was likely due to the inhibition of autophagy in viruses. The present study sought to evaluate the antiviral effect of NH4Cl in a model of several fish cells and zebrafish. The findings demonstrated that the administration of NH4Cl after viral infection inhibited the proliferation of a variety of fish viruses, encompassing both DNA and RNA viruses. Further studies have indicated that NH4Cl obstructed autophagy-dependent virus proliferation of spring viremia of carp virus (SVCV) by inhibiting autophagic flux. The molecular mechanism revealed that SVCV contributed to the polyubiquitination of interferon regulatory factor 3 (IRF3) and promoted the degradation of IRF3 through cargo receptor sequestosome 1 (SQSTM1/p62)-mediated selective autophagy. However, NH4Cl was observed to inhibit SVCV-mediated selective autophagy of IRF3, thereby facilitating the production of interferon. Furthermore, the SVCV N protein was of critical importance in this process. Nevertheless, NH4Cl impeded this degradation process by inhibiting the autophagy pathway. The study found that NH4Cl was highly efficacious in controlling fish virus infection both in vivo and in vitro. It can therefore be concluded that the antiviral effect of ammonia fertilizers was, at least in part, due to the inhibition of viral autophagy.

The antiviral activity of myricetin against pseudorabies virus through regulation of the type I interferon signaling pathway

The type I interferon signaling pathway constitutes a pivotal component of the innate immune response, encompassing the cGAS/STING and JAK/STAT pathways. Drugs that affect the body's innate immune response could potentially be used as broad-spectrum antivirals. In this study, the antiviral activities of 25 flavonoids against pseudorabies virus (PRV) were tested in PK-15 cells. Eight active flavonoids were identified, with IC50 values ranging from 23.24 to 323.09 µM. Subsequently, the regulatory effects of these flavonoids on the cGAS/STING pathway in PRV-infected cells were investigated. It was found that Myricetin significantly increased the transcriptional levels of cGAS, STING, IRF3, and IFN-β, which had been reduced by PRV infection. The regulation of the type I interferon signaling pathways by myricetin following PRV infection was further investigated through the production of cGAMP and the assessment of transcriptional and protein levels of pivotal genes and proteins. To confirm the activation of the innate immune response, a dual luciferase gene reporter study found that the expression of the IFN-β promoter in the myricetin-treated group was significantly elevated in a cellular model of type I interferon signaling pathway, and the contents of IFN-β were also significantly higher than those observed in the infected-untreated group in a PRV-infected mice model. Moreover, the transcriptional and protein levels of key genes and proteins in cell and mouse models exhibited analogous outcomes to those observed in PRV-infected cells. These findings suggest that myricetin can effectively activate the type I interferon signaling pathway, thereby enhancing the innate immune response during PRV infection.

IMPORTANCE

PRV, belonging to the Herpesviridae family, is an easily overlooked zoonotic pathogen that can threaten human health. The immunoprotective efficacy of conventional vaccines is significantly reduced due to the continuous mutation of the PRV genome, which constantly generates new viral strains. Therefore, there is a need to develop potent therapeutic drugs. PRV is capable of evading the host's natural immunity by suppressing the host's type I interferon signaling pathway, and the search for drugs that activate natural immunity can induce the body to produce type I IFN interferon and exert antiviral effects. Accordingly, the present study sought to identify active compounds from flavonoids that modulate the type I IFN interferon signaling pathway and thus inhibit the proliferation of PRV, which provides a new idea for the development of anti-PRV drugs from flavonoids that modulate the type I IFN interferon signaling pathway to enhance the body's antiviral immunity.

Histone demethylases in autophagy and inflammation

Autophagy dysfunction is associated with changes in autophagy-related genes. Various factors are connected to autophagy, and the mechanism regulating autophagy is highly complicated. Epigenetic changes, such as aberrant expression of histone demethylase, are actively associated not only with oncogenesis but also with inflammatory responses. Among post-translational modifications, histone lysine methylation holds significant importance. There are over 30 members of histone lysine demethylases (KDMs), which act as epigenetic regulators in physiological processes and diseases. Importantly, KDMs are abnormally expressed in the regulation of cellular autophagy and inflammation, representing a crucial mechanism affecting inflammation-related diseases. This article reviewed the function of KDMs proteins in autophagy and inflammation. Specifically, It focused on the specific regulatory mechanisms underlying the activation or inhibition of autophagy, as well as their abnormal expression in inflammatory responses. By analyzing each KDM in epigenetic modification, this review provides a reliable theoretical basis for clinical decision marking regarding autophagy abnormalities and inflammatory diseases.

The Strategies Used by Animal Viruses to Antagonize Host Antiviral Innate Immunity: New Clues for Developing Live Attenuated Vaccines (LAVs)

As an essential type of vaccine, live attenuated vaccines (LAVs) play a crucial role in animal disease prevention and control. Nevertheless, developing LAVs faces the challenge of balancing safety and efficacy. Understanding the mechanisms animal viruses use to antagonize host antiviral innate immunity may help to precisely regulate vaccine strains and maintain strong immunogenicity while reducing their pathogenicity. It may improve the safety and efficacy of LAVs, as well as provide a more reliable means for the prevention and control of infectious livestock diseases. Therefore, exploring viral antagonistic mechanisms is a significant clue for developing LAVs, which helps to explore more viral virulence factors (as new vaccine targets) and provides a vital theoretical basis and technical support for vaccine development. Among animal viruses, ASFV, PRRSV, PRV, CSFV, FMDV, PCV, PPV, and AIV are some typical representatives. It is crucial to conduct in-depth research and summarize the antagonistic strategies of these typical animal viruses. Studies have indicated that animal viruses may antagonize the antiviral innate immunity by directly or indirectly blocking the antiviral signaling pathways. In addition, viruses also do this by antagonizing host restriction factors targeting the viral replication cycle. Beyond that, viruses may antagonize via regulating apoptosis, metabolic pathways, and stress granule formation. A summary of viral antagonistic mechanisms might provide a new theoretical basis for understanding the pathogenic mechanism of animal viruses and developing LAVs based on antagonistic mechanisms and viral virulence factors.

Central SGLT2 mediate sympathoexcitation in hypertensive heart failure via attenuating subfornical organ endothelial cGAS ubiquitination to amplify neuroinflammation: Molecular mechanism behind sympatholytic effect of Empagliflozin

BACKGROUND

Sodium/glucose co-transporter 2 (SGLT2) inhibitors have transformed heart failure (HF) treatment, offering sympatholytic effects whose mechanisms are not fully understood. Our previous studies identified Cyclic GMP-AMP synthase (cGAS)-derived neuroinflammation in the Subfornical organ (SFO) as a promoter of sympathoexcitation, worsening myocardial remodeling in HF. This research explored the role of central SGLT2 in inducing endothelial cGAS-driven neuroinflammation in the SFO during HF and assessed the impact of SGLT2 inhibitors on this process.

METHODS

Hypertensive HF was induced in mice via Angiotensin II infusion for four weeks. SGLT2 expression and localization in the SFO were determined through immunoblotting and double-immunofluorescence staining. AAV9-TIE-shRNA (SGLT2) facilitated targeted SGLT2 knockdown in SFO endothelial cells (ECs), with subsequent analyses via immunoblotting, staining, and co-immunoprecipitation to investigate interactions with cGAS, mitochondrial alterations, and pro-inflammatory pathway activation. Renal sympathetic nerve activity and heart rate variability were measured to assess sympathetic output, alongside evaluations of cardiac function in HF mice.

RESULTS

In HF model mice, SGLT2 levels are markedly raised in SFO ECs, disrupting mitochondrial function and elevating oxidative stress. SGLT2 knockdown preserved mitochondrial integrity and function, reduced inflammation, and highlighted the influence of SGLT2 on mitochondrial health. SGLT2's interaction with cGAS prevented its ubiquitination and degradation, amplifying neuroinflammation and HF progression. Conversely, Empagliflozin counteracted these effects, suggesting that targeting the SGLT2-cGAS interaction as a novel HF treatment avenue.

CONCLUSION

This study revealed that SGLT2 directly reduced cGAS degradation in brain ECs, enhancing neuroinflammation in the SFO, and promoting sympathoexcitation and myocardial remodeling. The significance of the central SGLT2-cGAS interaction in cardiovascular disease mechanisms is emphasized.

PRRSV-2 nsp2 Ignites NLRP3 inflammasome through IKKβ-dependent dispersed trans-Golgi network translocation

The NLRP3 inflammasome is a fundamental component of the innate immune system, yet its excessive activation is intricately associated with viral pathogenesis. Porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2), belonging to the family Arteriviridae, triggers dysregulated cytokine release and interstitial pneumonia, which can quickly escalate to acute respiratory distress and death. However, a mechanistic understanding of PRRSV-2 progression remains unclear. Here, we screen that PRRSV-2 nsp2 activates the NLRP3 inflammasome, thereby instigating a state of hyperinflammation. Mechanistically, PRRSV-2 nsp2 interacts with the nucleotide-binding and oligomerization (NACHT) domain of NLRP3, augmenting IKKβ recruitment to driving NLRP3 translocation to the dispersed trans-Golgi network (dTGN) for oligomerization. This process facilitates ASC polymerization, culminating in the activation of the NLRP3 inflammasome. In addition, the IKKβ-dependent NLRP3 translocation to the dTGN is pivotal for pseudorabies virus (PRV) and encephalomyocarditis virus (EMCV)-induced inflammatory responses. Collectively, these results elucidate a novel mechanism of NLRP3 inflammasome activation during PRRSV-2 infection, providing valuable insights into PRRSV-2 pathogenesis.

Suppression of ZBP1-mediated NLRP3 inflammasome by the tegument protein VP22 facilitates pseudorabies virus infection

The interaction between Z-DNA binding protein 1 (ZBP1) and the NLR family pyrin domain-containing 3 (NLRP3) inflammasome has been uncovered in several viral infections. However, the role of this molecular pathway during infection with the alpha-herpesvirus pseudorabies virus (PRV) remains largely elusive. Here, we report that during PRV infection, ZBP1-mediated NLRP3 inflammasome activation is inhibited by the viral tegument protein VP22, thereby facilitating viral infection. Through a combination of RNA sequencing and genetic studies, we demonstrate that PRV VP22 functions as a virus-encoded virulence factor by evading the inhibitory effects of ZBP1 on virus infection. Importantly, the replication and pathogenicity of a recombinant PRV lacking VP22 are significantly increased in ZBP1-deficient cells and mice. Mechanistically, PRV VP22 interacts with ZBP1, impeding the recruitment of receptor-interacting protein kinase 3 and Caspase-8, thereby inhibiting NLRP3 activation. Furthermore, we show that the N-terminal 1-50 amino acid domain of VP22 dominantly destabilizes ZBP1-mediated function. Taken together, these findings identify a functional link between PRV infection and ZBP1-mediated NLRP3 inflammatory response, providing novel insights into the pathogenesis of PRV and other herpesviruses.

IMPORTANCE

Z-DNA binding protein 1 (ZBP1) functions as a pivotal innate immune sensor that regulates inflammatory cell death during viral infections. However, its role in pseudorabies virus (PRV) infection remains unknown. Here, we demonstrate that ZBP1 serves as a restrictive factor by triggering the activation of the NLR family pyrin domain-containing 3 inflammasome, a process counteracted by PRV-encoded protein VP22. Furthermore, VP22 interferes with the interaction between ZBP1 and receptor-interacting protein kinase 3/Caspase-8, particularly through its N-terminal 1-50 amino acids. Importantly, deficiency in ZBP1 enhances the replication and virulence of recombinant viruses lacking VP22 or its N-terminal 1-50 amino acids. These findings reveal how PRV escapes ZBP1-mediated inflammatory responses during infection, potentially informing the rational design of therapeutic interventions.

Evasion of the Antiviral Innate Immunity by PRV

Pseudorabies virus (PRV) establishes persistent latent infections by effectively evading the host's antiviral innate immune response. PRV has developed sophisticated strategies to bypass immune surveillance through coevolution with its host. Currently, no effective vaccine exists to prevent or treat infections caused by emerging PRV variants, and the interactions between PRV and the host's innate immune defenses remain incompletely understood. Nevertheless, ongoing research is uncovering insights that may lead to novel treatments and preventive approaches for herpesvirus-related diseases. This review summarizes recent advances in understanding how PRV disrupts key adaptors in immune signaling pathways to evade antiviral immunity. Additionally, we explored the intrinsic cellular defenses that play crucial roles in combating viral invasion. A deeper understanding of the immune evasion strategies of PRV could inform the development of new therapeutic targets and vaccines.

Insight into the Interaction Mechanism of Pseudorabies Virus Infection

The pseudorabies virus (PRV), also known as suid alphaherpesvirus 1 (SuAHV-1), has garnered significant attention due to its broad host range and the economic losses it incurs in the swine industry. This review aims to provide a comprehensive understanding of the intricate virus-host interactions during PRV infection, focusing on the evasion strategies of the virus against the host responses. We also summarize the mechanisms by which PRV manipulates the host cell machinery to facilitate its replication and spread, while simultaneously evading detection and clearance by the immune system. Furthermore, we discuss the latest advancements, such as metabolic, autophagic, and apoptotic pathways in studying these interactions, highlighting the role of various cellular factors and pathways in elucidating virus-host dynamics. By integrating these insights, the article aims to provide a comprehensive overview of the molecular mechanisms underlying PRV pathogenesis and host response, paving the way for the development of novel therapeutic strategies against this virus.

The loss of both pUL16 and pUL21 in HSV-1 infected cells abolishes cytoplasmic envelopment

Previously, we had developed synthetic genomics methods to assemble an infectious clone of herpes simplex virus type-1 (HSV-1). To do this, the genome was assembled from 11 separate cloned fragments in yeast using transformation associated recombination. The eleven fragments or "parts" spanned the 152 kb genome and recombination was achieved because of the overlapping homologous sequences between each fragment. To demonstrate the robustness of this genome assembly method for reverse genetics, we engineered different mutations that were located in distant loci on the genome and built a collection of HSV-1 genomes that contained single and different combination of mutations in 5 conserved HSV-1 genes. The five genes: UL7, UL11, UL16, UL21 and UL51 encode virion structural proteins and have varied functions in the infected cell. Each is dispensable for virus replication in cell culture, however, combinatorial analysis of deletions in the five genes revealed "synthetic-lethality" of some of the genetic mutations. Thus, it was discovered that any virus that carried a UL21 mutation in addition to the other gene was unable to replicate in Vero cells. Replication was restored in a complementing cell line that provided pUL21 in trans. One particular combination (UL16-UL21) was of interest because the proteins encoded by these genes are known to physically interact and are constituents of the tegument structure. Furthermore, their roles in HSV-1 infected cells are unclear. Both are dispensable for HSV-1 replication, however, in HSV-2 their mutation results in nuclear retention of assembled capsids. We thus characterized these viruses that carry the single and double mutant. What we discovered is that in cells where both pUL16 and pUL21 are absent, cytoplasmic capsids were evident but did not mature into enveloped particles. The capsid particles isolated from these cells showed significantly lower levels of incorporation of both VP16 and pUL37 when compared to the wild-type capsids. These data now show that of the tegument proteins, like the essential pUL36, pUL37 and VP16; the complex of pUL16 and pUL21 should be considered as important mediators of cytoplasmic maturation of the particle.

Retinol binding protein 4 restricts PCV2 replication via selective autophagy degradation of viral ORF1 protein

Autophagy is a highly conserved degradative process that has been linked to various functions, including defending host cells against pathogens. Although the involvement of autophagy in porcine circovirus 2 (PCV2) infection has become apparent, it remains unclear whether selective autophagy plays a critical role in PCV2 restriction. Here we show that retinol-binding protein 4 (RBP4), an adipokine for retinol carrier, initiates the autophagic degradation of PCV2 ORF1 protein. PCV2 infection increases RBP4 protein levels through MAPK-eIF4E axis in living cells. Ectopic expression of RBP4 or recombinant RBP4 treatment promotes the degradation of ORF1 protein. Mechanistically, RBP4 activates TRAF6 to induce K63-linked ubiquitination of ORF1, leading to SQSTM1/p62-mediated selective autophagy for degradation. Consequently, RBP4 deficiency increases viral loads and exacerbates the pathogenicity of PCV2 in vivo. Collectively, these results identify RBP4 as a key host restriction factor of PCV2 and reveal a previously undescribed antiviral mechanism against PCV2 in infected cells.

The multifaceted roles of selective autophagy receptors in viral infections

Selective autophagy is a protein clearance mechanism mediated by evolutionarily conserved selective autophagy receptors (SARs), which specifically degrades misfolded, misassembled, or metabolically regulated proteins. SARs help the host to suppress viral infections by degrading viral proteins. However, viruses have evolved sophisticated mechanisms to counteract, evade, or co-opt autophagic processes, thereby facilitating viral replication. Therefore, this review aims to summarize the complex mechanisms of SARs involved in viral infections, specifically focusing on how viruses exploit strategies to regulate selective autophagy. We present an updated understanding of the various critical roles of SARs in viral pathogenesis. Furthermore, newly discovered evasion strategies employed by viruses are discussed and the ubiquitination-autophagy-innate immune regulatory axis is proposed to be a crucial pathway to control viral infections. This review highlights the remarkable flexibility and plasticity of SARs in viral infections.

Disruption of herpes simplex virus type 2 pUL21 phosphorylation impairs secondary envelopment of cytoplasmic nucleocapsids

The multifunctional tegument protein pUL21 of HSV-2 is phosphorylated in infected cells. We have identified two residues in the unstructured linker region of pUL21, serine 251 and serine 253, as phosphorylation sites. Both phosphorylation sites are absent in HSV-1 pUL21, which likely explains why phosphorylated pUL21 was not detected in cells infected with HSV-1. Cells infected with HSV-2 strain 186 viruses deficient in pUL21 phosphorylation exhibited reductions in both cell-cell spread of virus infection and virus replication. Defects in secondary envelopment of cytoplasmic nucleocapsids were also observed in cells infected with viruses deficient in pUL21 phosphorylation as well as in cells infected with multiple strains of HSV-2 and HSV-1 deleted for pUL21. These results confirm a role for HSV pUL21 in the secondary envelopment of cytoplasmic nucleocapsids and indicate that phosphorylation of HSV-2 pUL21 is required for this activity. Phosphorylation of pUL21 was substantially reduced in cells infected with HSV-2 strain 186 mutants lacking the viral serine/threonine kinase pUL13, indicating a requirement for pUL13 in pUL21 phosphorylation.

IMPORTANCE

It is well known that post-translational modification of proteins by phosphorylation can regulate protein function. Here, we determined that phosphorylation of the multifunctional HSV-2 tegument protein pUL21 requires the viral serine/threonine kinase pUL13. In addition, we identified serine residues within HSV-2 pUL21 that can be phosphorylated. Phenotypic analysis of mutant HSV-2 strains with deficiencies in pUL21 phosphorylation revealed reductions in both cell-cell spread of virus infection and virus replication. Deficiencies in pUL21 phosphorylation also compromised the secondary envelopment of cytoplasmic nucleocapsids, a critical final step in the maturation of all herpes virions. Unlike HSV-2 pUL21, phosphorylation of HSV-1 pUL21 was not detected. This fundamental difference between HSV-2 and HSV-1 may underlie our previous observations that the requirements for pUL21 differ between HSV species.

AMPK/MTOR/TP53 Signaling Pathway Regulation by Calcitonin Gene-Related Peptide Reduces Oxygen-Induced Lung Damage in Neonatal Rats through Autophagy Promotion

Our previous studies indicated that calcitonin gene-related peptide (CGRP) alleviates hyperoxia-induced lung injury and suggested the possible involvement of autophagy in this process. Herein, we aimed to further explore the potential involvement of tumor protein p53 (TP53) and autophagy in the mode of action of CGRP against hyperoxia-induced lung injury in vitro and in vivo. The study conducted tests on type II alveolar epithelial cells (AECII) and rats that were subjected to hyperoxia treatment or combined treatment of hyperoxia with CGRP, CGRP inhibitor, rapamycin (an autophagy agonist), 3-methyladenine (3-MA, an autophagy inhibitor), TP53 silencing/inhibitor (pifithrin-α), or expression vector/activator (PRIMA-1 (2,2-bis(hydroxymethyl)-3-quinuclidinone)) and their corresponding controls. We found that oxidative stress, apoptosis, and autophagy were all increased by hyperoxia treatment in vitro. However, treating AECII cells with CGRP reversed hyperoxia-induced oxidative stress and apoptosis but further promoted autophagy. In addition, the combined treatment with rapamycin or TP53 silencing with CGRP promoted the effect of CGRP, while contrary results were obtained with combined therapy with 3-MA or TP53 overexpression. In vivo, the number of hyperoxia-induced autophagosomes was promoted in the lung tissue of neonatal rats. Furthermore, hyperoxia increased the expression levels of AMP-activated protein kinase (AMPK) alpha 1 (also known as protein kinase AMP-activated catalytic subunit alpha 1 (PRKAA1)) but inhibited TP53 and mechanistic target of rapamycin (MTOR); these expression trends were regulated by CGRP treatment. In conclusion, we showed that CGRP can attenuate hyperoxia-induced lung injury in neonatal rats by enhancing autophagy and regulating the TP53/AMPK/MTOR crosstalk axis.

Rehmmannia glutinosa polysaccharide exerts antiviral activity against pseudorabies virus and antioxidant activity

Pseudorabies virus (PRV) is an important pathogen harming the global pig industry. Vaccines available for swine cannot protect against PRV completely. Furthermore, no antiviral drugs are available to treat PRV infections. Rehmmannia glutinosa polysaccharide (RGP) possesses several medicinal properties. However, its antiviral activity is not reported. In the present study, we found that RGP can inhibit PRV/XJ5 infection by western blotting, immunofluorescent assay (IFA), and TCID50 assay quantitative polymerase chain reaction (qPCR). We revealed RGP can inhibit virus adsorption and invasion into PK-15 cells in a dose-dependent manner via western blotting, IFA, TCID50 assay, and quantitative polymerase chain reaction (qPCR), and suppressed PRV/XJ5 replication through western blotting, and qPCR. Additionally, it also reduced PRV/XJ5-induced ROS, lipid oxidation, and improved SOD levels in PK-15 cells, which was observed by using corresponding test kits. To conclude, our findings suggest that RGP might be a novel therapeutic agent for preventing and controlling PRV infection and antioxidant agent.

Pseudorabies virus VHS protein abrogates interferon responses by blocking NF-κB and IRF3 nuclear translocation

Herpesviruses antagonize host antiviral responses through a myriad of molecular strategies culminating in the death of the host cells. Pseudorabies virus (PRV) is a significant veterinary pathogen in pigs, causing neurological sequalae that ultimately lead to the animal's demise. PRV is known to trigger apoptotic cell death during the late stages of infection. The virion host shutdown protein (VHS) encoded by UL41 plays a crucial role in the PRV infection process. In this study, we demonstrate that UL41 inhibits PRV-induced activation of inflammatory cytokine and negatively regulates the cGAS-STING-mediated antiviral activity by targeting IRF3, thereby inhibiting the translocation and phosphorylation of IRF3. Notably, mutating the conserved amino acid sites (E192, D194, and D195) in the RNase domain of UL41 or knocking down UL41 inhibits the immune evasion of PRV, suggesting that UL41 may play a crucial role in PRV's evasion of the host immune response during infection. These results enhance our understanding of how PRV structural proteins assist the virus in evading the host immune response.

Lysosomal control of the cGAS-STING signaling

The cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway has a crucial role in combating pathogen infection. However, its aberrant activation is involved in several human disorders. Lysosomes are emerging as key negative regulators of cGAS-STING signaling. Here, we discuss the lysosomal control of cGAS-STING signaling and its implication in human disorders.

OTULIN's influence on neuroinflammation and pain modulation in trigeminal neuralgia

INTRODUCTION

Trigeminal neuralgia (TN), marked by chronic pain from neural damage, is closely associated with inflammation. The role of OTULIN, a key regulator in inflammation and autophagy, is not fully understood in TN. The regulatory mechanism of OTULIN, a key protein involved in modulating inflammatory responses and autophagy processes, remains incompletely elucidated, particularly in the context of TN and neuroinflammation.

METHODS

An infraorbital nerve ligation-induced rat model of TN was used. OTULIN's expression was modulated using adenovirus vectors and short hairpin RNA. The impact on pain and inflammatory responses was assessed via quantitative real-time polymerase chain reaction, western blot, immunofluorescence, and transcriptomic analysis.

RESULTS

Enhanced OTULIN expression significantly increased head withdrawal thresholds and reduced pain sensitivity and neuroinflammatory markers in the model. Conversely, silencing OTULIN exacerbated pain and inflammation. Transcriptomic data revealed OTULINs influence on both inflammatory and autophagy pathways, specifically in suppressing NLR family pyrin domain containing 3 (NLRP3) inflammasome and promoting autophagy. In vitro experiments demonstrated OTULIN's inhibition of inflammatory markers in microglia and neurons.

CONCLUSION

OTULIN is crucial in modulating TN, reducing neuropathic pain and neuroinflammation by activating the autophagy pathway and inhibiting the NLRP3 inflammasome.

Nervous necrosis virus capsid protein and Protein A dynamically modulate the fish cGAS-mediated IFN signal pathway to facilitate viral evasion

Nervous necrosis virus (NNV), an aquatic RNA virus belonging to Betanodavirus, infects a variety of marine and freshwater fishes, leading to massive mortality of cultured larvae and juveniles and substantial economic losses. The enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is widely recognized as a central component in the innate immune response to cytosolic DNA derived from different pathogens. However, little is known about the response of cGAS to aquatic RNA viruses. This study found that Epinephelus coioides cGAS (EccGAS) overexpression inhibited NNV replication, whereas EccGAS silencing promoted NNV replication. The anti-NNV activity of EccGAS was involved in interferon (IFN) signaling activation including tumor necrosis factor receptor-associated factor family member-associated NF-kappa-B activator-binding kinase 1 (TBK1) phosphorylation, interferon regulatory factor 3 (IRF3) nuclear translocation, and the subsequent induction of IFNc and ISGs. Interestingly, NNV employed its capsid protein (CP) or Protein A (ProA) to negatively or positively modulate EccGAS-mediated IFN signaling by simultaneously targeting EccGAS. CP interacted with EccGAS via the arm-P, S-P, and SD structural domains and promoted its polyubiquitination with K48 and K63 linkages in an EcUBE3C (the ubiquitin ligase)-dependent manner, ultimately leading to EccGAS degradation. Conversely, ProA bound to EccGAS and inhibited its ubiquitination and degradation. In regulating EccGAS protein content, CP's inhibitory action was more pronounced than ProA's protective effect, allowing successful NNV replication. These novel findings suggest that NNV CP and ProA dynamically modulate the EccGAS-mediated IFN signaling pathway to facilitate the immune escape of NNV. Our findings shed light on a novel mechanism of virus-host interaction and provide a theoretical basis for the prevention and control of NNV.IMPORTANCEAs a well-known DNA sensor, cGAS is a pivotal component in innate anti-viral immunity to anti-DNA viruses. Although there is growing evidence regarding the function of cGAS in the resistance to RNA viruses, the mechanisms by which cGAS participates in RNA virus-induced immune responses in fish and how aquatic viruses evade cGAS-mediated immune surveillance remain elusive. Here, we investigated the detailed mechanism by which EccGAS positively regulates the anti-NNV response. Furthermore, NNV CP and ProA interacted with EccGAS, regulating its protein levels through ubiquitin-proteasome pathways, to dynamically modulate the EccGAS-mediated IFN signaling pathway and facilitate viral evasion. Notably, NNV CP was identified to promote the ubiquitination of EccGAS via ubiquitin ligase EcUBE3C. These findings unveil a novel strategy for aquatic RNA viruses to evade cGAS-mediated innate immunity, enhancing our understanding of virus-host interactions.

TRIM26 facilitates PRV infection through NDP52-mediated autophagic degradation of MAVS

Pseudorabies virus (PRV) has evolved multiple strategies to evade host antiviral responses to benefit virus replication and establish persistent infection. Recently, tripartite motif 26 (TRIM26), a TRIM family protein, has been shown to be involved in a broad range of biological processes involved in innate immunity, especially in regulating viral infection. Herein, we found that the expression of TRIM26 was significantly induced after PRV infection. Surprisingly, the overexpression of TRIM26 promoted PRV production, while the depletion of this protein inhibited virus replication, suggesting that TRIM26 could positively regulate PRV infection. Further analysis revealed that TRIM26 negatively regulates the innate immune response by targeting the RIG-I-triggered type I interferon signalling pathway. TRIM26 was physically associated with MAVS independent of viral infection and reduced MAVS expression. Mechanistically, we found that NDP52 interacted with both TRIM26 and MAVS and that TRIM26-induced MAVS degradation was almost entirely blocked in NDP52-knockdown cells, demonstrating that TRIM26 degrades MAVS through NDP52-mediated selective autophagy. Our results reveal a novel mechanism by which PRV escapes host antiviral innate immunity and provide insights into the crosstalk among virus infection, autophagy, and the innate immune response.

Pseudorabies virus tegument protein US2 antagonizes antiviral innate immunity by targeting cGAS-STING signaling pathway

Background

The cGAS-STING axis-mediated type I interferon pathway is a crucial strategy for host defense against DNA virus infection. Numerous evasion strategies developed by the pseudorabies virus (PRV) counteract host antiviral immunity. To what extent PRV-encoded proteins evade the cGAS-STING signaling pathway is unknown.

Methods

Using US2 stably expressing cell lines and US2-deficient PRV model, we revealed that the PRV tegument protein US2 reduces STING protein stability and downregulates STING-mediated antiviral signaling.

Results

To promote K48-linked ubiquitination and STING degradation, US2 interacts with the LBD structural domain of STING and recruits the E3 ligase TRIM21. TRIM21 deficiency consistently strengthens the host antiviral immune response brought on by PRV infection. Additionally, US2-deficient PRV is less harmful in mice.

Conclusions

Our study implies that PRV US2 inhibits IFN signaling by a new mechanism that selectively targets STING while successfully evading the host antiviral response. As a result, the present study reveals a novel strategy by which PRV evades host defense and offers explanations for why the Bartha-K61 classical vaccine strain failed to offer effective defense against PRV variant strains in China, indicating that US2 may be a key target for developing gene-deficient PRV vaccines.

The precise function of alphaherpesvirus tegument proteins and their interactions during the viral life cycle

Alphaherpesvirus is a widespread pathogen that causes diverse diseases in humans and animals and can severely damage host health. Alphaherpesvirus particles comprise a DNA core, capsid, tegument and envelope; the tegument is located between the nuclear capsid and envelope. According to biochemical and proteomic analyses of alphaherpesvirus particles, the tegument contains at least 24 viral proteins and plays an important role in the alphaherpesvirus life cycle. This article reviews the important role of tegument proteins and their interactions during the viral life cycle to provide a reference and inspiration for understanding alphaherpesvirus infection pathogenesis and identifying new antiviral strategies.

Varicella-zoster virus-related neurological complications: From infection to immunomodulatory therapies

The Varicella-zoster virus (VZV), classified as a neurotropic member of the Herpesviridae family, exhibits a characteristic pathogenicity, predominantly inducing varicella, commonly known as chickenpox, during the initial infectious phase, and triggering the reactivation of herpes zoster, more commonly recognized as shingles, following its emergence from a latent state. The pathogenesis of VZV-associated neuroinflammation involves a complex interplay between viral replication within sensory ganglia and immune-mediated responses that contribute to tissue damage and dysfunction. Upon primary infection, VZV gains access to sensory ganglia, establishing latent infection within neurons. During reactivation, the virus can spread along sensory nerves, triggering a cascade of inflammatory mediators, chemokines, and immune cell infiltration in the affected neural tissues. The role of both adaptive and innate immune reactions, including the contributions of T and B cells, macrophages, and dendritic cells, in orchestrating the immune-mediated damage in the central nervous system is elucidated. Furthermore, the aberrant activation of the natural defence mechanism, characterised by the dysregulated production of immunomodulatory proteins and chemokines, has been implicated in the pathogenesis of VZV-induced neurological disorders, such as encephalitis, myelitis, and vasculopathy. The intricate balance between protective and detrimental immune responses in the context of VZV infection emphasises the necessity for an exhaustive comprehension of the immunopathogenic mechanisms propelling neuroinflammatory processes. Despite the availability of vaccines and antiviral therapies, VZV-related neurological complications remain a significant concern, particularly in immunocompromised individuals and the elderly. Elucidating these mechanisms might facilitate the emergence of innovative immunomodulatory strategies and targeted therapies aimed at mitigating VZV-induced neuroinflammatory damage and improving clinical outcomes. This comprehensive understanding enhances our grasp of viral pathogenesis and holds promise for pioneering therapeutic strategies designed to mitigate the neurological ramifications of VZV infections.

The MGF300-2R Protein of African Swine Fever Virus Promotes IKKβ Ubiquitination by Recruiting the E3 Ubiquitin Ligase TRIM21

African swine fever (ASF) is an acute, hemorrhagic, highly contagious disease in pigs caused by African swine fever virus (ASFV). Our previous study identified that the ASFV MGF300-2R protein functions as a virulence factor and found that MGF300-2R degrades IKKβ via selective autophagy. However, the E3 ubiquitin ligase responsible for IKKβ ubiquitination during autophagic degradation still remains unknown. In order to solve this problem, we first pulled down 328 proteins interacting with MGF300-2R through immunoprecipitation-mass spectrometry. Next, we analyzed and confirmed the interaction between the E3 ubiquitin ligase TRIM21 and MGF300-2R and demonstrated the catalytic role of TRIM21 in IKKβ ubiquitination. Finally, we indicated that the degradation of IKKβ by MGF300-2R was dependent on TRIM21. In summary, our results indicate TRIM21 is the E3 ubiquitin ligase involved in the degradation of IKKβ by MGF300-2R, thereby augmenting our understanding of the functions of MGF300-2R and offering insights into the rational design of live attenuated vaccines and antiviral strategies against ASF.

Harmol used for the treatment of herpes simplex virus induced keratitis

Herpes simplex virus type 1 (HSV-1) infection of the eyes results in herpes simplex keratitis (HSK), which has led to vision loss and even blindness in patients. However, the rate of drug resistance in HSV is on the rise; therefore, new antiviral agents with sufficient safety profiles must be developed. At present, we assessed the anti-HSV-1 activity of 502 natural compounds and their ability to reduce the HSV-1-induced cytopathic effect. We chose harmol for further studies because it exhibited the highest antiviral activity. We found that harmol inhibited both HSV-1 F and HSV-1/153 (a clinical drug-resistant strain) replication, with an EC50 of 9.34 µM and 5.84 µM, respectively. Moreover, harmol reduced HSV-1 replication in corneal tissues and viral progeny production in tears, and also alleviated early corneal surface lesions related to HSK. For example, harmol treatment preserved corneal thickness and nerve density in HSK mice. Interestingly, harmol also showed a promising antiviral effect on HSV-1/153 induced HSK in mouse model. Furthermore, harmol combined with acyclovir (ACV) treatment showed a greater antiviral effect than either one alone in vitro. Therefore, harmol may be a promising therapeutic agent for managing HSK.

Pseudorabies virus usurps non-muscle myosin heavy chain IIA to dampen viral DNA recognition by cGAS for antagonism of host antiviral innate immunity

Alphaherpesvirus pseudorabies virus (PRV) causes severe economic losses to the global pig industry and has garnered increasing attention due to its broad host range including humans. PRV has developed a variety of strategies to antagonize host antiviral innate immunity. However, the underlying mechanisms have not been fully elucidated. In our previous work, we demonstrated that non-muscle myosin heavy chain IIA (NMHC-IIA), a multifunctional cytoskeleton protein, attenuates innate immune responses triggered by RNA viruses. In the current study, we reported a previously unrecognized role of NMHC-IIA in counteracting PRV-induced cyclic GMP-AMP synthase (cGAS)-dependent type I interferon (IFN-I) production. Mechanistically, PRV infection led to an elevation of NMHC-IIA, strengthening the interaction between poly (ADP-ribose) polymerase 1 (PARP1) and cGAS. This interaction impeded cGAS recognition of PRV DNA and hindered downstream signaling activation. Conversely, inhibition of NMHC-IIA by Blebbistatin triggered innate immune responses and enhanced resistance to PRV proliferation both in vitro and in vivo. Taken together, our findings unveil that PRV utilizes NMHC-IIA to antagonize host antiviral immune responses via impairing DNA sensing by cGAS. This in-depth understanding of PRV immunosuppression not only provides insights for potential PRV treatment strategies but also highlights NMHC-IIA as a versatile immunosuppressive regulator usurped by both DNA and RNA viruses. Consequently, NMHC-IIA holds promise as a target for the development of broad-spectrum antiviral drugs.IMPORTANCECyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) axis plays a vital role in counteracting alphaherpesvirus infections. Alphaherpesviruses exploit various strategies for antagonizing cGAS-STING-mediated antiviral immune responses. However, limited examples of pseudorabies virus (PRV)-caused immunosuppression have been documented. Our findings reveal a novel role of non-muscle myosin heavy chain IIA (NMHC-IIA) in suppressing PRV-triggered innate immune responses to facilitate viral propagation both in vitro and in vivo. In detail, NMHC-IIA recruits poly (ADP-ribose) polymerase 1 (PARP1) to augment its interaction with cGAS, which impairs cGAS recognition of PRV DNA. Building on our previous demonstration of NMHC-IIA's immunosuppressive role during RNA virus infections, these findings indicate that NMHC-IIA acts as a broad-spectrum suppressor of host antiviral innate immunity in response to both DNA and RNA viruses. Therefore, NMHC-IIA will be a promising target for the development of comprehensive antiviral strategies.

IDI1 inhibits the cGAS-Sting signaling pathway in hepatocellular carcinoma

Metabolic reprogramming is one of the prominent features that distinguishes tumor cells from normal cells. The role of metabolic abnormalities in regulating innate immunity is poorly understood. In this study, we found that IDI1 is significantly upregulated in liver cancer. IDI1 has no significant effect on the growth or invasion of liver cancer cells but significantly promotes liver cancer development in mice. Through molecular mechanism studies, we found that IDI1 interacts with the important regulator of innate immunity cGAS and recruits the E3 ligase TRIM41 to promote cGAS ubiquitination and degradation, inhibiting the cGAS-Sting signaling pathway. IDI1 inhibits the phosphorylation of TBK1 and the downstream factor IRF3 as well as the expression of CCL5 and CXCL10. In summary, this study revealed the important role of the metabolic enzyme IDI1 in the regulation of innate immunity, suggesting that it may be a potential target for liver cancer treatment.

Inhibition of pseudorabies virus replication via upregulated interferon response by targeting 7-dehydrocholesterol reductase

Pseudorabies virus (PRV) is an alpha-herpesvirus capable of infecting a range of animal species, particularly its natural host, pigs, resulting in substantial economic losses for the swine industry. Recent research has shed light on the significant role of cholesterol metabolism in the replication of various viruses. However, the specific role of cholesterol metabolism in PRV infection remains unknown. Here, we demonstrated that the expression of 7-dehydrocholesterol reductase (DHCR7) is upregulated following PRV infection, as evidenced by the proteomic analysis. Subsequently, we showed that DHCR7 plays a crucial role in promoting PRV replication by converting 7-dehydrocholesterol (7-DHC) into cholesterol, leading to increased cellular cholesterol levels. Importantly, DHCR7 inhibits the phosphorylation of interferon regulatory factor 3 (IRF3), resulting in reduced levels of interferon-beta (IFN-β) and interferon-stimulated genes (ISGs). Finally, we revealed that the DHCR7 inhibitor, trans-1,4-bis(2-chlorobenzylaminomethyl) cyclohexane dihydrochloride (AY9944), significantly suppresses PRV replication both in vitro and in vivo. Taken together, the study has established a connection between cholesterol metabolism and PRV replication, offering novel insights that may guide future approaches to the prevention and treatment of PRV infections.

Pathogenicity and immunogenicity of a quadruple gene-deleted pseudorabies virus variant as a vaccine candidate

Since late 2011, the PRV variants have emerged in China, characterized by the increased virulence. The traditional attenuated vaccines have proven insufficient in providing complete protection, resulting in substantial economic losses to swine industry. In this study, a vaccine candidate strain, ZJ01-ΔgI/gE/TK/UL21, carrying the quadruple gene deletion was derived from the previously generated three gene-deleted virus ZJ01-ΔgI/gE/TK. As anticipated, piglets inoculated with ZJ01-ΔgI/gE/TK/UL21 exhibited normal body temperatures and showed no viral shedding, consistent with the observations from piglets treated with ZJ01-ΔgI/gE/TK. Importantly, a significant higher level of interferon induction was observed among piglets in the ZJ01-ΔgI/gE/TK/UL21 group compared to those in the ZJ01-ΔgI/gE/TK group. Upon challenge with the PRV variant ZJ01, piglets immunized with ZJ01-ΔgI/gE/TK/UL21 exhibited reduced viral shedding compared to the ZJ01-ΔgI/gE/TK group. Furthermore, piglets vaccinated with ZJ01-ΔgI/gE/TK/UL21 exhibited minimal pathological lesions in brain tissues, similar to those in the ZJ01-ΔgI/gE/TK group. These results underscore the potential of ZJ01-ΔgI/gE/TK/UL21 as a promising vaccine for controlling PRV infection.

Listerin promotes cGAS protein degradation through the ESCRT pathway to negatively regulate cGAS-mediated immune response

The enzyme cyclic GMP-AMP synthase (cGAS) is a key sensor for detecting misplaced double-stranded DNA (dsDNA) of genomic, mitochondrial, and microbial origin. It synthesizes 2'3'-cGAMP, which in turn activates the stimulator of interferon genes pathway, leading to the initiation of innate immune responses. Here, we identified Listerin as a negative regulator of cGAS-mediated innate immune response. We found that Listerin interacts with cGAS on endosomes and promotes its K63-linked ubiquitination through recruitment of the E3 ligase TRIM27. The polyubiquitinated cGAS is then recognized by the endosomal sorting complexes required for transport machinery and sorted into endosomes for degradation. Listerin deficiency enhances the innate antiviral response to herpes simplex virus 1 infection. Genetic deletion of Listerin also deteriorates the neuroinflammation and the ALS disease progress in an ALS mice model; overexpression of Listerin can robustly ameliorate disease progression in ALS mice. Thus, our work uncovers a mechanism for cGAS regulation and suggests that Listerin may be a promising therapeutic target for ALS disease.

Autophagy as a dual-faced host response to viral infections

Autophagy selectively degrades viral particles or cellular components, either facilitating or inhibiting viral replication. Conversely, most viruses have evolved strategies to escape or exploit autophagy. Moreover, autophagy collaborates with the pattern recognition receptor signaling, influencing the expression of adaptor molecules involved in the innate immune response and regulating the expression of interferons (IFNs). The intricate relationship between autophagy and IFNs plays a critical role in the host cell defense against microbial invasion. Therefore, it is important to summarize the interactions between viral infections, autophagy, and the host defense mechanisms against viruses. This review specifically focuses on the interactions between autophagy and IFN pathways during viral infections, providing a comprehensive summary of the molecular mechanisms utilized or evaded by different viruses.

Identification of new conserved linear B-cell epitopes in the 3AB and 3C protein of Senecavirus A

Senecavirus A (SVA) is a member of the Picornaviridae family, Senecavirus genus. The outbreak of swine vesicular disease caused by SVA has presented a significant threat to pig husbandry and public health, resulting in substantial economic losses. In this study, recombinant SVA 3AB and 3C proteins were expressed in the prokaryotic system, purified, and utilized to generate eight monoclonal antibodies (mAbs) specific to SVA 3AB or 3C proteins. Three B-cell epitopes recognized by these mAbs were subsequently identified by Western blotting. The mAbs 3G3, 3D6, and 3B7 against 3AB recognize the epitope ⁹⁰NAYDGPKKNS¹⁰⁰; the mAbs 2C10, 2C8, and 2D12 against 3C recognize the epitope ⁷⁵FTHHGLPTDL⁸⁵, and the mAbs 3C4 and 4A11 against 3C recognize the epitope ⁹⁵DQMPARNSRV¹⁰⁵. Moreover, all three epitopes are highly conserved in different SVA strains and are exposed on the surface of 3AB or 3C proteins, potentially representing important B-cell epitopes. This study constitutes the first report of SVA nonstructural protein epitopes, which may be beneficial for developing innovative detection methods and vaccines and for investigating the roles of 3AB and 3C in viral replication.